Method for separating alkali metal ions from alkoxylates

ABSTRACT

Alkali metal ions are separated off from alkoxylates containing alkali metal ions by a process comprising:  
     a) dilution of the alkali metal-containing alkoxylate with an inert solvent,  
     b) treatment of the alkali metal-containing solution of the alkoxylate with a cationic exchanger in order to obtain a substantially alkali metal-free solution of the alkoxylate, and  
     c) removal of the solvent from the substantially alkali metal-free solution of the alkoxylate in order to obtain a substantially alkali metal-free and substantially solvent-free alkoxylate.

[0001] The present invention relates to a process for separating alkalimetal ions from alkoxylates containing alkali metal ions, alkalimetal-free alkoxylates and a process for the preparation of alkalimetal-free alkoxylates.

[0002] Alkoxylates, in particular polyalkylene oxides and adducts ofalkylene oxides with alcohols and/or alkylphenols, are usually preparedunder alkali metal hydroxide catalysis. Depending on the intended use,it is frequently necessary to remove the catalyst as completely aspossible from the adduct. This is the case, for example, withalkoxylates which are used as fuel additives or carrier oils in fueladditive packets or formulations. Such alkoxylates for carrier oils arein general adducts of propylene oxide and/or butylene oxide withalcohols and/or alkylphenols of more than 6 carbon atoms, which areprepared by catalysis using potassium hydroxide. In order to ensuresubstantially residue-free combustibility of the carrier oils, thecatalyst must be separated off. In the conventional processes, this isdone by neutralization and precipitation as acidic potassium phosphateand subsequent filtration. After the synthesis of the alkoxylates, alsoreferred to here generally as polyethers, it is therefore necessary toneutralize the potassium alcoholate contained in the product with dilutephosphoric acid (stoichiometric amounts of phosphoric acid dissolved inabout 10%, based on the reactor content, of water) and to distill offthe water for crystallization of the acidic potassium phosphate. Thereactor content must then be filtered, for example through a batchwisesheet filter, which is manually loaded and scraped off. Further requiredsteps are the separation and separate packing of product-moist salt andimpregnated filter sheets, their transport and incineration; thecleaning of the reactors before the subsequent batch, also in the caseof a batch procedure, in order to remove remaining phosphate residueswhich neutralize marked amounts of catalyst and can thus delay or evensuppress initiation of the oxyalkylation reaction; the drying of thereactors for the subsequent batch. It is clear that the removal of thecatalyst is expensive. Moreover, the carrier oils thus obtained stillcontain small amounts of potassium and also phosphorus, so thatresidue-free combustion of the carrier oils is not possible.

[0003] It is an object of the present invention to provide alkoxylateswhich are substantially free of catalyst impurities from thepreparation.

[0004] It is a further object of the present invention to provide aprocess for the preparation of alkoxylates which are substantially freeof catalyst impurities from the preparation.

[0005] It is a further object of the present invention to provide aprocess for separating the catalyst from alkoxylates, which permitssubstantial removal of the catalyst from the product and preferablyavoids contamination of the product with phosphate.

[0006] We have found that this object is achieved by the novel processfor the separation of alkali metal ions from alkoxylates containingalkali metal ions (in particular potassium and sodium ions), whichcomprises the following steps:

[0007] a) dilution of the alkali metal-containing alkoxylate with aninert solvent,

[0008] b) treatment of the alkali metal-containing solution of thealkoxylate with a cation exchanger for exchanging alkali metal ions forhydrogen ions in order to obtain a substantially alkali metal-freesolution of the alkoxylate, and

[0009] c) removal of the solvent from the substantially alkalimetal-free solution of the alkoxylate in order to obtain a substantiallyalkali metal-free and substantially solvent-free alkoxylate.

[0010] In the novel process for the preparation of alkoxylates, thealkoxylates are initially prepared in a conventional manner, and thecatalyst is then removed by the novel process for separating off alkalimetal.

[0011] The term alkali metal-free or substantially alkali metal-freemeans that less than 5, preferably less than 1, ppm of alkali metal ionsare present. The alkali metal-containing alkoxylate to be purifiedgenerally contains from 5 000 to 100, in particular from 2 000 to 1 000,ppm of alkali metal ions.

[0012] The term substantially solvent-free means that the alkoxylatecontains <1 000, preferably <500, ppm of solvent.

[0013] The term alkoxylate includes pure substances as well as mixtureswhich are obtained using different alkylene oxides and/or differentalcohols.

[0014] The term alkoxylate includes polyalkylene oxides (polyethers) andalcohol- and/or alkylphenol-initiated polyethers. The polyether or thepolyether moiety of the alcohol- and/or alkylphenol-initiated polyethersis generally composed of at least one C₂-C₆-alkylene oxide, inparticular ethylene oxide, propylene oxide, n-butylene oxide,2,3-butylene oxide and/or isobutylene oxide. In general, at least oneC₁-C₅₀-alkanol, preferably C₂-C₂₀-alkanol, particularly preferablyC₆-C₁₄-alkanol, in particular 2-ethylhexanol, nonanol, isononanol,tridecanol, isotridecanol, etc., is used as the alcohol. The alkylphenolused is in general a C₁-C₅₀-alkylphenol, particularly preferably aC₆-C₁₄-alkylphenol, preferably a C₆-C₁₄-alkylphenol, in particularnonylphenol, octylphenol or dodecylphenol, or a di-C₁-C₅₀-alkylphenol.

[0015] Alkanol-initiated polyethers having from about 10 to 35,preferably from about 15 to 30, alkylene oxide units are preferred.

[0016] The preparation of alkoxylates is known per se. Polyethersyntheses are described, for example, in Ullmann's Encyclopedia ofIndustrial Chemistry, 5th Edition, Vol. 21, 1992, 579-589, and thepublications stated therein. The preparation of alcohol- oralkylphenol-initiated polyethers is described, for example, in Ullmann'sEnzyklopädie der technischen Chemie, 4th Edition, Volume 22, 491-492 andVolume 19, 31-33.

[0017] The catalyst-containing crude alkoxylate product is initiallydiluted with an inert solvent for removal of the catalyst. Solvents usedare in general an aliphatic or cyclic ether, such as tert-butyl methylether, tetrahydrofuran or dioxane, a hydrocarbon, such as pentane,hexane, toluene or xylene, a ketone, such as acetone or methyl ethylketone, and preferably an alcohol, in particular a C₁-C₄-alkanol, suchas ethanol, isopropanol, n-butanol, isobutanol and preferably methanol.For removal of the alkali metal catalyst, the dilute solution is treatedwith a cation exchanger, for example is passed through an exchanger bed,in particular in the form of a column, or is stirred with the cationexchanger. Particularly suitable cation exchangers are strongly acidic,macroporous resins, for example those based on crosslinked polystyreneshaving sulfonic esters as functional groups.

[0018] The amount of cation exchanger required for removal of thecatalyst is dependent on the catalyst content of the product to betreated and on the capacity of the ion exchanger used.

[0019] The solvent is then removed again, for example by distilling off.The removal is preferably effected in two steps. In a first step, themain amount of the solvent is removed, preferably by distilling off, analkoxylate solution depleted of solvent and the solvent being obtained.In the first step, preferably at least 80% and up to 95% of the solventare removed. In a second step, the remaining amount of the solvent isremoved, preferably by stripping the depleted solution of the alkoxylatewith inert gas in a column, in order to obtain a substantially alkalimetal-free and substantially solvent-free alkoxylate and alcohol.

[0020] After a specific operating time, the cation exchanger needs to beregenerated. The regeneration is preferably integrated in the overallprocess, i.e. alkoxylate solution still contained in the cationexchanger is recovered before the regeneration and is recycled to stagec) or a) of the catalyst separation process. Any residues of thealkoxylate solution which still adhere to the cation exchanger areremoved by washing with the inert solvent. The wash solvent is likewiserecycled to stage a) of the catalyst separation process.

[0021] The regeneration of the cation exchanger preferably comprises thefollowing steps:

[0022] d1) removal of the alkoxylate solution from the cation exchangerand, if required, washing of the cation exchanger with the inertsolvent; this can be effected in such a way that the alkoxylate solutionis removed, for example by discharging, and the cation exchanger is thenwashed with the solvent; alternatively the solvent can be fed in withoutprior removal of the alkoxylate solution, until the alkoxylate has beenwashed out,

[0023] d2) if required, washing of the cation exchanger withdemineralized water,

[0024] d3) regeneration of the cation exchange resin with an acid,preferably sulfuric acid,

[0025] d4) washing the cation exchange resin neutral with demineralizedwater,

[0026] d5) washing out the water present in the ion exchanger resin withan inert solvent, preferably a water-miscible inert solvent, and

[0027] d6) if required, loading of the cation exchanger with the inertsolvent desired for the treatment with the cation exchanger.

[0028] The inert solvent used in the regeneration of the cationexchanger is preferably the same as that also used in the catalystseparation process. Step d6) is then omitted.

[0029] Preferably, the alkoxylate adducts are stripped with steam or aninert gas, such as nitrogen, after the synthesis, i.e. before step a) ofthe novel process.

[0030] The present invention can be particularly advantageously used forseparating potassium ions from adducts of ethylene oxide and/orpropylene oxide and/or butylene oxide, in particular propylene oxideand/or butylene oxide, with C₆-C₁₄-alcohols and/or C₆-C₁₄-alkylphenols,the inert solvent used preferably being a C₁-C₄-alkanol, in particularmethanol.

[0031] A preferred embodiment of the present invention is describedbelow. The stated amounts of solvent/diluent and temperature ranges arepreferred values for separating potassium from propylene oxide/butyleneoxide adducts using methanol as a diluent. They may assume differentvalues in the case of other adducts, catalysts and solvents, but theoptimum values can be readily determined by a person skilled in the artusing routine methods.

[0032] For dilution of the potassium-containing adduct (step a),preferably from 5 to 25, particularly about 15, % (m/m) of methanol areadded to the adduct. The methanolic solution is then treated with acation exchanger, for example is passed over an ion exchanger bed whichcontains a cation exchanger. It is possible to use a commercial ionexchange resin, preferably in granular form. For example, theabovementioned ion exchangers, for example Lewatit SP 120 (Bayer) andAmberlite 252 C (Rohm and Haas), are suitable.

[0033] The service life of the cation exchanger is in general 1 year orlonger. On passing through the ion exchanger, the methanolic solution ispreferably at from about 20 to 60° C., particularly 45 preferably about50° C. The cation exchanger is present in the acidic form. During thepassage of the potassium-containing methanolic solution of the adduct itbinds potassium ions and releases protons according to the followingequation:

R—O—(CHR′—CHR″—O)_(x)—K++IEXH+

R—O—(CHR′—CHR″—O)_(x)—H++IEXK+

[0034] IEX=ion exchanger

[0035] R=alkyl or alkylaryl

[0036] R′═R″=H, CH₃, C₂H₅

[0037] After the treatment with the cation exchanger, the methanolicadduct solution is greatly depleted of potassium, in particularsubstantially potassium-free, and particularly preferably theconcentration of the potassium ions is not more than 1 ppm.

[0038] For separating off possible fine fractions of the ion exchangeresin, the solution is then filtered in a conventional manner. Beforethe further treatment, it may be temporarily stored in a container.

[0039] It is advisable for the potassium content of the adduct solutionleaving the ion exchanger to be monitored continuously or at least atregular intervals by means of analytical measurement. In the event of abreakthrough of potassium ions the exchanger must be regenerated. Thisis done by means of an acid, preferably sulfuric acid, particularlypreferably about 5% strength sulfuric acid, by the following procedure:

[0040] First, the feed stream of the potassium-containing methanolicsolution of the adduct to the ion exchanger is stopped. Then, methanolcan be fed in in order to wash the ion exchanger product-free.Adduct-containing methanol, which in turn is used for diluting the crudeproduct, i.e. the catalyst-containing alkoxylate, is obtained. However,before the washing with methanol, the potassium-free adduct solutionstill present in the ion exchanger is preferably forced out of the ionexchanger with nitrogen or another inert gas and is combined with theother potassium-free adduct solution for the further treatment. The ionexchanger is then washed product-free with methanol, and the washmethanol leaving the ion exchanger and containing a small amount ofadduct is used for diluting the potassium-containing crude product.Preferably, the wash or rinse methanol is also preferably filtered toseparate off possible fine fractions of the ion exchange resin beforebeing used further.

[0041] The potassium-laden ion exchanger is now full of methanol, whichhas to be removed before the regeneration. One possible method is towash the ion exchanger with demineralized water by the countercurrent orcocurrent method. The methanol-containing wastewater obtained here isnot used further but is disposed of via a wastewater treatment plant. Inorder to avoid relatively large losses of methanol, it is, however,preferable to remove the methanol, for example to force it out of theion exchanger by means of an inert gas, such as nitrogen, before washingthe ion exchanger with demineralized water. This methanol is preferablycombined with the other, adduct-containing rinse methanol and is usedagain for diluting subsequent batches of potassium-containing adducts.

[0042] The ion exchanger is then converted back into the acidic form bypassing through dilute sulfuric acid (1 to 20% by weight), preferablyabout 5% strength sulfuric acid, by the countercurrent method. This isfollowed by washing neutral with demineralized water, and the water isfinally washed out with methanol, preferably by the trickle-bedprocedure. The resulting aqueous methanol phase can be used instead offresh methanol for preliminary cleaning of reactors on product change.

[0043] After complete replacement of the water by methanol, the ionexchanger is ready for operation again and can be loaded again.

[0044] The substantially potassium-free adduct solution leaving the ionexchanger is further treated as follows:

[0045] For reasons relating to application technology, the solution mustbe freed from the solvent as completely as possible. This is preferablycarried out in an evaporator unit, in particular a single-stage one,with connected stripping column. The preferred temperature range is fromabout 150 to 170° C., particularly preferably 160° C. First, the mainamount of the methanol, preferably at least 80%, is separated off bydistillation. The recovered methanol can be collected and reused.

[0046] In particular an inert gas stripping column in which theconcentration is reduced to methanol contents of less than 1 000 ppm,preferably less than 500 ppm, is used for removing the remainingmethanol from the adduct solution. The inert gas is preferably nitrogen.

[0047] The methanol stripped off in the stripping column can also bereused. The substantially potassium-free desired products having a lowmethanol content and leaving the stripping column are preferably passedthrough a heat exchanger, where they preheat the adduct solution havinga low potassium content, before entry into the evaporator apparatus andare themselves cooled to about 50 to 60° C.

[0048] The novel process comprises a plurality of process steps in whichpure methanol is required, i.e. in washing the ion exchanger free ofproduct, in washing the water out of the ion exchanger and in fillingthe ion exchanger with methanol after the regeneration and, if required,for diluting the crude product prior to separating off the potassium inthe ion exchanger. The methanol distilled off and stripped off ispreferably reused for this purpose. For diluting thepotassium-containing crude product, adduct-containing methanol from thewashing out of the ion exchanger is preferably additionally orexclusively reused.

[0049] In the drawings:

[0050]FIG. 1 shows a flow diagram of an ion exchange unit as used forcarrying out the novel process and

[0051]FIG. 2 shows a flow diagram of an evaporator unit downstream ofthe ion exchange unit and intended for separating off the diluentmethanol.

[0052] The invention is described in detail on the basis of aparticularly preferred embodiment with reference to the figures.

[0053] As can be seen in FIG. 1, the crude, potassium-containing,methanol-diluted alkoxylates (butylene oxide adduct with isotridecanol)are transported via the line 3 by means of the pump P20 over a cationexchanger bed 2 in the container 1. In the container, an ion exchangeresin is installed between two sieve plates. The ion exchanger isinitially present in acidic form and binds potassium ions with releaseof protons. The dilution of the alkoxylates with methanol is necessaryin order to achieve substantially complete cation exchange. Themethanol-diluted alkoxylates entering the container 1 have a temperatureof about 50° C.

[0054] The alkoxylate solution emerging from the container 1 via line 4is substantially potassium-free. It passes through the filter F10 forseparating off possible fine fractions of the exchange resin and is thentemporarily stored in the container 5.

[0055] By analytical measurement, the alkoxylate stream leaving thecontainer 1 is constantly monitored for freedom from potassium. In theevent of a breakthrough of potassium ions, the exchanger must beregenerated. This is done using about 5% strength sulfuric acid by thefollowing procedure:

[0056] The feed stream of the crude alkoxylate to the container 1 isstopped; the methanol-diluted alkoxylate still remaining in theexchanger container is then forced into the container 5 by means ofnitrogen. The ion exchanger in the container 1 is then washedproduct-free with methanol, which is transported from container 6 vialine 7 with the pump P21; the container 1 is then emptied again byforcing in nitrogen. The resulting, alkoxylate-containing rinse methanolpasses through the filter F10 into the container 8 and is used again fordiluting subsequent batches of the crude alkoxylates in the reactors ofthe synthesis plant.

[0057] After replacement of the alkoxylate in the ion exchanger bymethanol, the container 1 is emptied as completely as possible into thecontainer 8, and the ion exchange resin is then washed by thecountercurrent method with demineralized water, which is fed in via line9. The resulting wastewater which still contains methanol in the initialfractions is disposed of via line 10.

[0058] After a pure water phase is present in the container 1, theregeneration of the laden ion exchange resin is carried out by passingthrough about 5% strength sulfuric acid by the countercurrent method vialine 11. The ion exchanger is converted back into the acidic form, and adilute solution of potassium sulfate, potassium bisulfate and sulfuricacid leaves the container 1 and is disposed of via line 10.

[0059] After complete regeneration, the ion exchanger fill is washedacid-free with demineralized water via line 9, the container 1 is thenagain emptied as completely as possible and residual water is replacedby methanol. The methanol required for this purpose is transported bymeans of the pump P21 from the container 6.

[0060] The aqueous methanol phases obtained in this process step aretransferred via line 12 into the container 13 and temporarily stored andare used in the synthesis of the alkoxylates instead of fresh methanolfor preliminary cleaning of reactors on product change.

[0061] After complete replacement of the water by methanol, the ionexchanger in the container 1 is ready for operation again and can beloaded again with methanolic alkoxylate solutions via the pump P20.

[0062] The methanol-containing and substantially potassium-freealkoxylates temporarily stored in the container 5 are then freed ascompletely as possible from the solvent.

[0063] This is done in a downstream single-stage evaporator unit withsubsequent nitrogen stripping column at about 160° C. (FIG. 2):

[0064] Substantially potassium-free alkoxylate solution is transportedfrom the container 5 by means of the pump P26 via line 14 into theforced-circulation evaporator 15, with which the evaporator reboiler 16is coordinated. The methanol is partially separated off by a procedurein which the vapor of the evaporator reboiler 16 is condensed in thecondenser 17 and is collected in the methanol container 6.

[0065] From the evaporator reboiler 16, the alkoxylated depleted ofmethanol and at about 160° C. is fed to the top of the column 18 and isstripped countercurrently with nitrogen, which is fed in via line 19.

[0066] The waste gas leaving the column 18 via line 20 is disposed ofafter separating off condensable fractions (methanol), which arelikewise collected in the container 6.

[0067] From the bottom of column, substanially methanol-free alkoxylateis taken off via line 21 and is used or stored.

[0068] The novel ion exchange process has the following advantages overthe phosphate precipitation process of the prior art:

[0069] After the synthesis of the alkylene oxide adducts with alcoholsby catalysis with potassium hydroxide, a number of process steps areomitted:

[0070] neutralization of the potassium alcoholate with dilute phosphoricacid and distilling off the water for crystallization of the acidicpotassium phosphate,

[0071] filtration of the reactor content through a batchwise sheetfilter which is manually loaded and scrapped off,

[0072] separation and separate packing of product-moist salt andimpregnated filter sheets and transport for residue incineration,

[0073] cleaning of the reactors before the subsequent batch, also in thebatch procedure, in order to remove remaining phosphate residues whichneutralize marked amounts of catalyst and can thus delay or suppressinitiation of the oxyalkylation reaction,

[0074] drying of the reactors for the subsequent batch, in the novelprocess in combination with the catalyst preparation of this lot.

[0075] The novel process permits economically and environmentallyfriendly purification of alkoxylates, in particular of carrier oils, atleast to products of high quality. The novel ion exchange process givescarrier oils which undergo combustion without residues in the engine andhave no emissions of additional foreign substances. Moreover, the novelprocess permits a capacity increase, which is substantially due to thefact that the reactors are available exclusively for the process of thesynthesis of the alkylene oxide adducts.

We claim:
 1. A process for separating alkali metal ions from alkoxylates containing alkali metal ions, comprising: a) dilution of the alkali metal-containing alkoxylate with an inert solvent, b) treatment of the alkali metal-containing solution of the alkoxylate with a cationic exchanger in order to obtain a substantially alkali metal-free solution of the alkoxylate, and c) removal of the solvent from the substantially alkali metal-free solution of the alkoxylate in order to obtain a substantially solvent-free alkoxylate containing less than 5 ppm alkali metal ions, which process includes a regeneration of the cation exchanger, the regeneration comprising the following steps: d1) removal of the alkoxylate solution from the cation exchanger and washing out the cation exchanger with an inert solvent, d2) if required, washing out the cation exchanger with demineralized water, d3) regeneration of the cation exchange resin with an acid, d4) washing the cation exchange resin neutral with demineralized water, d5) washing out the water present in the ion exchange resin with an inert solvent and d6) if required, loading of the cation exchanger with the inert solvent desired for the treatment with the cation exchanger, wherein in step d1) the alkoxylate solution is removed from the cation exchanger by forcing it out by means of an inert gas.
 2. A process as claimed in claim 1, wherein the removal of the solvent is effected in two steps, wherein firstly c1) the main amount of the solvent is removed in order to obtain an alkoxylate solution depleted of solvent and then c2) the remaining amount of the solvent is removed from the alkoxylate solution depleted of the solvent, in order to obtain a substantially alkali metal-free and substantially solvent-free alkoxylate.
 3. A process as claimed in claim 2, wherein the solvent is distilled off in step c1) and/or the remaining amount of the solvent is removed by stripping with inert gas in step c2).
 4. A process as claimed in any of claims 1 to 3, wherein the alkoxylate is an adduct of ethylene oxide and/or propylene oxide and/or butylene oxide with at least one C₁-C₅₀-alkanol and/or at least one (C₁-C₅₀-alkyl)phenol.
 5. A process as claimed in any of claims 1 to 4, wherein the alkali metal ions to be separated off are potassium ions.
 6. A process as claimed in any of claims 1 to 5, wherein the solvent used for diluting the alkoxylate and/or in the regeneration of the cation exchanger is a C₁-C₄-alkyl alcohol, preferably methanol.
 7. A process as claimed in any of claims 1 to 6, wherein, in step b), an alkoxylate solution having an alkali metal content of not more than 1 ppm is obtained. 